Telegraphic transmitter



June 19, 1928.

E. W. ENGSTROM 'PBLEGRAPHIC TRANSMITTER Filed Feb. 11, 1927 PatentedJune 19 1928.

UNITED STATES 1,674,505 PATENT OFFICE.

mm W. nnos'rnou, or SCHENECTAIDY, NEW YORK, ASSIGNOB r0 ennnm unc- TRIGCOMPANY, A CORPORATION OF NEW YORK.

TELEGBAPHIC TRANSMITTER.

Application filed February 11, 1927. Serial No. 167,568.

My invention relates to telegraphic transmitters employing vacuum tubeoscillatlon generators in which theanode potential for the generator issupplied from any su1table source through appropriate smoothing means.

' In systems of this type and particularly where the anode potentlal issupplied through rectifying valves, it is common to employ as asmoothing means, condensers connected in shunt with the circuit andreactors connected in series with the circuit. Because ofthe useof shuntcondensers in the smoothin system and because of the vary-- ing impeance of the oscillation generator with keying, and particularly 1n highspeed telegraphic transmitters where the anode current of theoscillation generator rapidly varies with keying, conditions foroscillatory transients exist and such transients occur at the points ofchanging current. The use of smoothing reactors in these systems is11mited in that they delay the flow of direct current to the oscillationgenerator and'ln that they are conducive to the transient conditionmentioned. This is particularly true if the smoothing reactor beconnected on the load side of the last shunt condenser. In telegraphictransmitters of the type to be described, it is common to have the lastelement of the smoothin system consist of a shunt condenser andrequently shunt condensers are relied upon altogether for the necessarysmoothing. This, however, does not remedy the situation since atransient condition upon closing the signal key remains preventingsatisfactory operation of the system, particularly at high speeds.

The object of my invention is to overcome the above mentioneddisadvantages and to provide a transmitting system which, among otherthings, may be operated at high speeds, in which the transmitted signalis of desirable wave shape and in which the anode supply issubstantially free from transient conditions.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Fig. 1 represents a transmittingcircuit to which my invention has been applied and Figs. 2 and 3 showthe effect of my invention upon the anode current characteristic of theoscillation enerator.

With reference to ig. 1 of the drawing, 1 indicates the usual threeelement electron discharge device which is employed as an oscillationgenerator having its anode and grid connected through condensers 2 tothe oscillatory circuit 3 which is associated with the antenna or otherload circuit 4. Connected to the grid circuit of this device is thecircuit 5 in which is connected the keying device one side of which is'connected to ground or to cathode potential. This keying device isrepresented as made u of a condenser" with a contact making nected inshunt thereto, although any of the well-known keying devices may beemployed.

The anode potential for the device 1 is' supplied from the alternatingcurrent source 7 through a transformer 8 and rectifyi valves 9. and 10,these valves being associafi in the circuit in a well-known manner. 11represents a smoothing means such as a condenser which is connecteddirectly across the direct current lines leading from the rectifyingvalves. Itfwill be understood, however, that my invention is not limitedto this particular arrangement since it applies equally to other systemswhere smoothing means are employed. 12 is the usual radio frequencychoke. Connected in the circuit between the smoothing means 11, and theoscillation generatorI empoy a reactance 14 for the purpose ofeliminating transient or surge conditions. This reactance is made up ofcomparatively few turns of conducting wire wound upon an iron corehaving alow re: luctance flux path. With such a construction at thefrequency of the usual ripple which exists in this circuit the devicewill have substantially no smooth effect but when a transient or surgecon ition arises the inductance will diminish the amplitude of thetransient as to substantially eliminate its undesirable effects u on thecircuit.

The a vantages of a reactance of this typev may best be understood byreference to 2 and 3. In Fig. '2 I have shown a curve representing thecharacteristic of the plate current in the anode circuit of the device 1before my reactance is inserted and Fig. 8

be sufiiciently great tosoey 6 conrepresents this same characteristic ina circuit in which my reactance is employed. In Fig.- 2, it will benoted that the'direct current upon the initial closing of the key 6 isseveral times greater than that of the normal current flowing when thecontact is closed. This transient is usually of an oscillatory natureand of high frequency. It produces anunsatisfactory wave shape in thesignal which is transmitted to the antenna andmay result in injury tothe equipment. By the use of a reactance constructed as "above :I havefound that it is' possible to eliminate this transient condition as isapparent from the characteristic shown in Fig; 3, and at the same timenot incur the undesirable effects incident to the use of the usualsmoothing reactors, as for example, transients in the circuit uponopening the key 6 andretardation in the flow of current to the anode ofthe device 1 upon the closing of the key. I 'prefer to term thisreactance a surge reactor since by virtue of its construction its onlyeffect in the circuit is during surge conditions.

Due to the capacity effect of this reactance it is desirable to connectit in the circuit between the radio frequency choke 12 and the potentialsource, thereby isolating it from the high frequency currents of theoscillation generator. For the same reason it may also be preferable toconnectit in the grounded side of the circuit.v f

While I have illustrated and described a single embodiment ofmyinvention,- I do 'not wish to bellimited to the specific circuitarrangement shown, as it will be "apparent that many variations may bemade in the circuit arrangement and the apparatus em-' .ployed withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim as new and desire to secure by Letters Patent of theUnitedStates, is

1. In a telegraphic transmitter employing a vacuum tube oscillationgenerator having an anode, a source of potential for said anode, asmoothing system associated with said-source, of potential and a surgereactor connected between said 's'moothing system and said oscillationgenerator, said surge reactor comprising a coil of lowinductance woundupon a core of low reluctance, said inductance and reluctance being suchas to produce no appreciable retarding effect upon the initiation ofnormal anode current,

whereby surges will be substantially eliminated. 4

2. In a telegraphic transmitter employ- ,ing a vacuum tube oscillationgenerator havc0 ing an anode a source of potential for said anode,smoothing means associated with said source of potential including shuntcapacity and a surge reactor, connected in the circuit between saidsmoothin means and said os- 05 cillation generator, sai surge reactorcompI'iSlllg a coil of low inductance wound upon a core of lowreluctance, said inductance and reluctance bein such as to produce noappreciable retar 'ng effect upon the initiation of normal anodecurrentwhereby surges willv be substantially. eliminated 3. In atelegraphic transmitter employing a vacuum tube oscillation generatorhaving an anode, a source of direct current potential for said anodecomprising an alternating current source and rectifying means associatedwith said alternating current source, a smoothing condenser connectedacross the circuit of said rectifying means, and a surge reactorconnected between said smoothing condenser and said oscillationgenerator, sa d surge reactor comprismg a coil of low Inductance woundupon a core of low reluctance, said inductance and s5 reluctance beingsuch as toproduce no appreciable retarding effect upon the initiation ofnormal anode current, whereby surges will be substantiall eliminated.

4; In a telegrap ic transmitter em loy- 9ov ing a vacuumtube'oscillation generator ving an anode circuit and a grid 'circuit, ameans in said grid circuit for keying said transmitter, a source ofdirect current potential for said anode circuit comprising analternating current source and rectifying ,means associated w1th saidalternating current source, a smoothing condenser connected across thecircuit Of said rectifying means and a surge reactor con- 10o inductanceandreluctance being such as to 108 produce no appreciable retardingefl'ectupon the intiation of normal 1 anode current,

whereby surges will be substantially elimi-. nated.

In witness whereof, I have hereunto set 1 10 my hand this 10th day ofFebruary, 1927.

ELDER W. ENGSTBOM I

